@article { ISI:000236784200028, title = {Finite size effects on the structural and magnetic properties of sol-gel synthesized NiFe2O4 powders}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {302}, number = {1}, year = {2006}, month = {JUL}, pages = {190-195}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Nanoparticles of nickel ferrite have been synthesized by the sol-gel method and the effect of grain size oil its structural and magnetic properties have been Studied in detail. X-ray diffraction (XRD) studies revealed that all the samples are single phasic possessing the inverse spinel structure. Grain size of the sol-gel synthesized powders has been determined from the XRD data and the strain graph. A grain size of 9 nm was observed for the as prepared powders of NiFe2O4 obtained through the sol-gel method. It was also observed that strain was induced during the firing process. Magnetization measurements have been carried out on all the samples prepared in the present series. It was found that the specific magnetization of the nanosized NiFe2O4 powders was lower than that of the corresponding coarse-grained counterparts and decreased with a decrease in grain size. The coercivity of the sol-gel synthesized NiFe2O4 nanoparticles attained a maximum value when the grain size was 15 nm and then decreased as the grain size was increased further. (c) 2005 Elsevier B.V. All rights reserved.

}, keywords = {grain size, magnetic properties, Nanoparticles, Nickel ferrite, strain}, issn = {0304-8853}, doi = {10.1016/j.jmmm.2005.08.029}, author = {George, M. and John, A. M. and Nair, S. S. and Joy, Pattayil Alias and Anantharaman, Maliemadom R.} } @article { ISI:000236477800029, title = {Size-dependent magnetic properties of nanocrystalline yttrium iron garnet powders}, journal = {Journal of Magnetism and Magnetic Materials}, volume = {301}, number = {1}, year = {2006}, month = {JUN}, pages = {212-219}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Yttrium iron garnet (YIG) powders with particle sizes of 9, 14, 25 and 60 nm have been synthesised and their magnetic properties have been studied as a function of particle size and temperature. The particles with sizes of 9 and 14 nm exhibited superparamagnetism. The blocking temperature (T-B) decreased with decreasing particle size, whereas the anisotropy constant (K) increased. The saturation magnetisation (M-s) decreased with decreasing particle size. These variations are attributed to large surface-to-volume ratios in nanoparticles where the surface moments are predominant. (c) 2005 Published by Elsevier B.V.

}, keywords = {anisotropy constant, Magnetism, Nanoparticles, Superparamagnetism, YIG}, issn = {0304-8853}, doi = {10.1016/j.jmmm.2005.06.027}, author = {Rajendran, M. and Deka, Sasanka and Joy, Pattayil Alias and Bhattacharya, Asish K.} } @article { ISI:000261061100016, title = {Magnetic and Mossbauer spectroscopic studies of NiZn ferrite nanoparticles synthesized by a combustion method}, journal = {Hyperfine Interactions}, volume = {183}, number = {1-3}, year = {2008}, month = {APR}, pages = {99-107}, publisher = {SPRINGER}, address = {VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS}, abstract = {

The properties of nanocrystalline Ni(0.5)Zn(0.5)Fe(2)O(4) synthesized by an auto-combustion method have been investigated by magnetic measurements and Mossbauer spectroscopy. The as-synthesized single phase nanosized ferrite powder is annealed at different temperatures in the range 673-1,273 K to obtain nanoparticles of different sizes. The powders are characterized by powder X-ray diffraction, vibrating sample magnetometer, transmission electron microscopy and Mossbauer spectroscopy. The as-synthesized powder with average particle size of similar to 9 nm is superparamagnetic. Magnetic transition temperature increases up to 665 K for the nanosized powder as compared to the transition temperature of 548 K for the bulk ferrite. This has been confirmed as due to the abnormal cation distribution, as evidenced from room temperature Mossbauer spectroscopic studies.

}, keywords = {Ferrite, magnetic properties, Mossbauer spectroscopy, Nanoparticles}, issn = {0304-3843}, doi = {10.1007/s10751-008-9736-3}, author = {Sreeja, V. and Vijayanand, S. and Deka, Sasanka and Joy, Pattayil Alias} } @article { ISI:000271843400019, title = {Ferromagnetic properties of glucose coated Cu2O nanoparticles}, journal = {Solid State Communications}, volume = {149}, number = {47-48}, year = {2009}, month = {DEC}, pages = {2199-2201}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

Magnetic properties of glucose coated cuprous oxide nanoparticles of different sizes have been studied. Unlike bulk Cu2O, which shows diamagnetic behavior, the nanoparticles show superparamagnetic behavior. A superparamagnetic blocking temperature of 21 K is observed for 5 nm particles. A magnetic hysteresis loop with a coercivity of 406 Oe is observed for these particles at 5 K. The magnetization and the coercivity increase with decreasing particle size. The superparamagnetic behavior, along with the increase in magnetization and coercivity with decreasing particle size, is due to the enhanced surface contributions to the magnetism. (C) 2009 Elsevier Ltd. All rights reserved.

}, keywords = {Chemical synthesis, Cuprous oxide, magnetic properties, Nanoparticles}, issn = {0038-1098}, doi = {10.1016/j.ssc.2009.09.013}, author = {Mahajan, Mangesh B. and Pavan, M. S. and Joy, Pattayil Alias} } @article { ISI:000300591700013, title = {Effect of inter-particle interactions on the magnetic properties of magnetite nanoparticles after coating with dextran}, journal = {International Journal of Nanotechnology}, volume = {8}, number = {10-12, SI}, year = {2011}, month = {JAN}, pages = {907-915}, publisher = {INDERSCIENCE ENTERPRISES LTD}, address = {WORLD TRADE CENTER BLDG, 29 ROUTE DE PRE-BOIS, CASE POSTALE 896, CH-1215 GENEVA, SWITZERLAND}, abstract = {

Nanoparticles of magnetite (Fe3O4) are synthesised by a coprecipitation method and coated with the biocompatible polymer, dextran. The uncoated and dextran coated magnetite nanoparticles are characterised by powder X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and magnetic measurements. The magnetic properties of the uncoated and coated magnetite nanoparticles are compared to study the effect of inter-particle magnetic interactions on the magnetic characteristics. Absence of magnetic hysteresis at room temperature indicates the superparamagnetic nature of the two samples. Evidence for the effect of reduced inter-particle magnetic interactions is directly obtained from the field dependence of magnetisation at room temperature. The decreased superparamagnetic blocking temperature and the nature and shape of the field cooled magnetisation curve of the dextran coated sample further confirmed that the inter-particle magnetic interactions are completely suppressed after coating.

}, keywords = {dextran coating, magnetic interactions, magnetic properties, magnetite, Nanoparticles}, issn = {1475-7435}, author = {Sreeja, V. and Joy, Pattayil Alias} } @article {43836, title = {Role of base fluid on the thermal conductivity of oleic acid coated magnetite nanofluids}, journal = {COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS}, volume = {529}, year = {2017}, month = {SEP}, chapter = {922-929}, abstract = {

Thermal conductivity enhancement of nanofluids of oleic acid coated magnetite nanoparticles dispersed in four different base fluids (toluene, xylene, mesitylene, kerosene) is studied to understand the role of the solvent (base fluid). From the correlation of the thermophysical properties of the base fluid with the thermal conductivity of the corresponding nanofluid, it is found that the nanofluid with the base fluid of lower intrinsic thermal conductivity and dielectric constant shows relatively larger enhancement in the thermal conductivity. A linear increase in the thermal conductivity with increasing viscosity is observed for all four nanofluids studied. The concentration dependent thermal conductivity studies showed enhancement only above a particular concentration, within the sensitivity of the measurement, and this critical concentration is different for the different nanofluids. The nanofluid with kerosene showed the lowest critical concentration for thermal conductivity enhancement compared to the other nanofluids. The difference between the experimental thermal conductivity and the calculated value using the Maxwell model is found to depend on the critical concentration. By assuming the critical concentration as the zero concentration, it is found that all the studied nanofluids almost follow the Maxwell model of thermal conductivity. Thus, for the dispersions of the same oleic acid coated magnetite nanoparticles, the base fluid affects the critical concentration for thermal conductivity enhancement, probably due to the interfacial effects arising from the surfactant-solvent interactions.

}, keywords = {Brownian-Motion, Enhancement, Heat-transfer Characteristics, Magnetic nanofluids, Maxwell model, Nanoparticles, Particle Migration, Size, stability, Suspension, Temprature, Thermal conductivity, Thermophysical properties, transport mechanism, viscosity}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2017.06.084}, author = {Lenin, Ramanujam and Joy, Pattayil Alias} }